To my understanding, the longer a barrel is, the higher the muzzle velocity, right?

So am I correct in saying that just like different calibres, the action is set differently in order to change the fps to keep them sub 12ft/lb. The same applies to barrel lengths to match the muzzle velocities???

and if the the two barrel lengths have exactly the same set up then the longer one must have a higher muzzle velocity even if it is only fractional?